A multi-wavelength laser light source includes a gain waveguide having a gain medium and a first mirror; and a waveguide wavelength filter, wherein the waveguide wavelength filter comprises: a first optical waveguide coupled to an end of the gain waveguide opposite to the first mirror, a plurality of ring resonators having input ports coupled to the first optical waveguide and having resonance wavelengths different from each other, a plurality of output waveguides coupled to respective output ports of the plurality of ring resonators, and second mirrors configured to correspondingly reflect, back to the plurality of ring resonators, at least part of light that has traveled via the output waveguides from the plurality of ring resonators.